Offshore platform

ABSTRACT

A method for joining two or more jacket or substructure components of an offshore platform in the water to form a single jacket unit. An offshore platform is located in deep water by dividing a jacket or support of extensive length therefor into at least two sections which have only sufficient buoyancy to float at water surface when the sections are launched from at least a vessel at a selected location. The sections are aligned and connected together. Guide means ensure proper alignment of the legs of the sections. Access tubes from the surface of the water to the hollow legs permit direct internal welding in securing the legs of the sections together. The sections are then sunk at the selected location until the jacket is in an upright position at which point it is anchored by driving piling through the jacket&#39;&#39;s hollow legs into the sea floor, following which the deck of the platform is placed or stabbed on the anchored jacket.

United States Patent [1 Guy et al. 1

[ OFFSHORE PLATFORM [75] Inventors: Arthur L. Guy, Houston, Tex.; JohnB. Reber, .lr., Sabah, Malaysia [73] Assignee: Exxon Production ResearchCompany, Houston, Tex.

[22] Filed: Oct. 1, 1973 [21] Appl. No.: 402,661

Related US. Application Data [63] Continuation-impart of Ser. No.286,374, Sept. 5,

1972, abandoned.

[451 Jan. 14, 1975' 9 Primary Examiner-Jacob Shapiro Attorney, Agent, orFirm-John S. Schneider [5 7] ABSTRACT A method for joining two or morejacket or substructure components of an offshore platform in the waterto form a single jacket unit. An offshore platform is located in deepwater by dividing a jacket or support of extensive length therefor intoat least two sections which have only sufficient buoyancy to float atwater surface when the sections are launched from at least a vessel at aselected location. The sections are aligned and connected together.Guide means ensure proper alignment of the legs of the sections. Accesstubes from the surface of the water to the hollow legs permit directinternal welding in securing the legs of the sections together. Thesections are then sunk at the selected location until the jacket is inan upright position at which point it is anchored by driving pilingthrough the jackets hollow legs into the sea floor, following which thedeck of the platform is placed or stabbed on the anchored jacket.

14 Claims, 17 Drawing Figures POWER WINCH PATENTEB W I 3.859.806

SHEET 1- UF 4 I LOWER CTION I 43 20A FIG. I.

UPPERHSECTION 5 o- I? aim u 1:

20B SEA OC K FIG. 2.

' 3 28 PEPE Q 208 v L.Y 208 I6 CAJBLE 3 PATENTEDJAN14'975 3,859,806

3min BM 4 72' ACCESS TUBE ACCESSITUBE DIAP RAGM Fl 7 ,/-ACCESSITUBELATCH SLOTS LATCHES T7 PATENTEB JAN I 4 I975 SHEET l BF 4 OFFSHOREPLATFORM CROSS-REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part of application Ser. No. 286,374 entitled OffshorePlatform Location" filed Sept. 5, 1972 by Arthur L. Guy et al and nowabandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention is directed to offshore structures which are fabricated at apoint remote from the point where they are ultimately located. Moreparticularly, the invention is concerned with a method and apparatus forunitizing an offshore jacket of extensive length for an offshoreplatform and locating same at a selected location. In its more specificaspects, the invention is directed to method and apparatus for use inextremely deep waters where an offshore platform is supported forvarious purposes such as, but not limited to, well drilling, productionof oil and gas, storage of oil and the like, and supporting navigationalaids and the like.

2. Description of the Prior Art It has been known for many years thatstructures may be located in deep waters by making the structuresbuoyantand floating them to a selected location in a body of water either in anassembled or non-assembled condition. To accomplish this, however, whereheavy seas may be encountered and long tows may be necessary, excessbuoyancy, as much as 35 percent or more, must be built into thestructure, which for aplatform jacket or support in waters of 500, 750,1000 feet or more may require flotation members each of which may be aslarge as a submarine.

It has also been known that flotation tanks may be added to sections ofan offshore structure and the sections gradually added one on top ofeach other until the completed structure is above water level. Anotherpossible method is to build an offshore structure close to land inshallow water or on land and add buoyant sections to it as the structureof increasing height is skidded or towed farther and farther to sea intodeeper water until the desired location is reached.

It has been disclosed in the prior art that supporting members foroffshore structures may be sealed by frangible or flexible (rupturable)diaphragms to maintain columns free of debris and to confer buoyancythereto.

The art has also described the floating of an offshore structure to anoffshore location on a barge and then launching it and sinking it at aselected point. This, too, is attendant with difficulties because theusual barge is only about 300 to 400 feet in length, and while largerbarges may be built, the greater the length the greater are the problemstherewith.

The art has, in addition; described fabricating an offshore structure atone location in sections, floating the sections on one or more vesselsor barges, launching the sections into water at or near another locationfor positioning the offshore platform, aligning and connecting thesections together and then sinking the connected sections to form asupport for a platform.

SUMMARY OF THE INVENTION The present invention may be briefly describedand summarized as involving a method for utilizing a sectional offshorejacket to support an offshore platform deck and locating the unitizedjacket at a selected loca tion. In the present invention, the jacket (ordeck support) to be located in deep water is fabricated on shore or at alocation remote from its ultimate position. Due to its extensive lengthwhich may range from 500 to 1500 or even more feet, the jacket isfabricated in a plurality of sections designed to interconnect with eachother at sea and form a unitary structure. Each section of the jacketisprovided with sufficient buoyance to float but insufficient buoyanceto be practical for a long tow (say one of more than I00 miles) or onein rough seas. On launching a section it shouldbe floating so that it isjust awash but still may support workmen to install equipment for movingor pulling the sections together and to perform other tasks which may benecessary. A part of this pulling equipment may be preinstalled, but itmay be removable after it has performed its designed service.

After the sections have bee'naligned and then moved or pulled together,the sections are fixedly connected together first by bolting and then bywelding. Guide means ensure proper alignment of the legs of the sectionsprior to fastening such legs together. The legs of the sections areconnectable together at both the waters surface and fully submerged.After the bolting of flanges the geometry of the sections form aninternal habitat for welding the legs of the sections together. Nooutside cofferdam is needed at the waters surface or fully submerged topermit welding of the legs together. Conventional welding is conductedinternally within the legs of the sections. Man'sized access tubesextend from above the surface of the water to each leg (at the waterssurface and fully submerged) of either section adjacent the connectionof the commonleg of the sections to permit a welder(s) to enter each legand weld the sections of each leg together from the interior of thejoint thus connecting the sections together structurally at atmosphericpressure. Such a weld develops the full strength of the adjacent pipe:sections. Then with the unitized jacket, without deck, floatinghorizontally, the pulling equipment may be removed and motor driven seacocks connected to power means. The

power means may be located on the jacket section or on a separate vesselas may be desired.

The sea cocks are opened and the unitized jacket rotates from horizontalto vertical as it sinks, the upper end being supported or lifted asflooding takes place by a crane on a barge or other vessel to ensureproper location. Thereafter pilings are driven through the hollow legsinto water bottom and the unitized jacket is anchored. The crane thenlifts and lowers or stabs a prefabricated deck having depending; meansinto the open legs of the unitized jacket or other means provided toreceive the supporting depending means from the platform. Thereafter,the deck may be used as desired for oil and/or gas production, storage,navigational aids, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be furtherdescribed by reference to the drawings in which:

FIG. 1 is a side elevational view of ajacket in two sections in thecourse of launching;

FIG. 1A is a cross-sectional view of the upper section taken on linelA-lA.

FIG. 2 illustrates the alignment of the two sections preparatorytoconnection or unitization;

FIG. 3 shows the connected unitized sections being rotated and sunk;

FIG. 4 illustrates the placement of a deck on the unitized structureafter anchoring by driving piling through I the legs into water bottom;

FIG. 5 is a detail of a quick connection means on each of the legs ofthe sections of the jacket shown on a surface leg;

FIG. 5A shows an access tube connection into a submerged leg;

FIG. 6 is a detail of fixed connection means and sealing means in eachleg of each jacket section for providing buoyancy; I

FIG. 7 is a detail of sea cocks for providing a flooding means;

FIG. 8 is a detail of an upper end of one leg of a jacket section and ashowing of a junction box for control of sea cocks;

FIG. 9 shows a portion of the upper and lower sections connectedtogether and means for connecting the control lines to the sea cocks;and

FIGS. 10 to show the steps of connecting the jacket sections togetherusing modified quick connection guide means and illustrating the mannerin which the legs of the sections may be welded together.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawingand particularly to FIG. 1, numeral 11 designates an upper jacketsection for an offshore structure which has been launched from a bargeor vessel such as 12 into a body of water 13 which may be, for example,1,000 feet in depth but which may be from about 500 to about 1,500 feetor more deep. Numeral l4 designates a second jacket section (hereinafterreferred to as the lower jacket section) which is designed to matinglyengage with upper jacket section 11 and form a unitized jacket structureas will be described. The sections 11 and 14 are fabricated on shore orat a point remote from which they are launched to be connected togetherand have only sufficient buoyancy to float substantially awash, suchthat little excess buoyancy is provided. Therefore, due to the length ofthe jacket sections 11 and 14 they are transported on barge 12 to theplace of launching and location; otherwise if they were fabricated inone piece for towing or in sections for towing, excess buoyancy in therange from about 30 percent to about 40 percent would have to beprovided to ensure stability and integrity of the structure.

The jacket sections 11 and 14 may have any desired number of legs, asfor example, three legs, four legs (as illustrated herein) or eight legsand are provided with transverse and cross struts l5 and 16 and otherbracing as necessary to provide rigidiy to the structure. The legs 20A(surface legs) and 20B (submerged legs) of both jacket sections 11 and14 are at least in part hollow to provide buoyancy and a passageway forthe piling used to anchor the unitized jacket to the ocean floor and forpermitting mans access for purposes of welding the joint connecting thelegs of the sections. The mating ends of the legs 20A and 20B at eachsection 11 and 14 are provided with connector flanges 22 which are to bebolted or otherwise connected togetherwhen the two sections are broughttogether.

Referring now to FIG. 2, a work barge 23 provided with a crane means 24and an auxiliary power supply means 25 is moved on location and isoperably connected to the lower section 14 by lift lines 26 formaneuvering the sections together. At this time a removable power winchmeans 27 is attached to the upper side structure of section 11 and bymeans of a cable 28 passing over a sheave or pulley 29 and attached tothe lower section 14 as shown provides means for pulling the twosections together. A flexible power supply conduit (not shown) is thenconnected between the winch 27 and the power supply means 25 on barge23.

A pre-alignment and latching means generally designated as 30 (see FIG.5) is provided to align and latch the two sections together just priorto the mating engagement of the flange 22. Means 30 consists of a latchprong 31 attached to the structure of section, 11 and a latching sleeve32 (provided with a flared bell shaped opening 33) which is attached tothe structure of section 14. As the two sections are brought togetherthe prong 31 enters the sleeve 32 and correctly aligns the flanges 22.The prong is latched in the sleeve by a spring biased latch in housing34. A means 30 may be positioned adjacent each of the legs 20A and 20Bof the two sections; however, only two means 30 may be used if they arepositioned on legs diagonally spaced apart.

The flanges 22 'of upper section 11 are provided on their connectingsurfaces with hard rubber gaskets 35 to protect the surface of theflange during engagement operations. Such gaskets may also be providedon the flanges of section 14 is desired and, apart from protection, alsocompensate for any slight misalignment. The flanges 22 are then boltedand welded together at each leg 20A and 208 to unitize the two sections11 and 14 and provide a single jacket generally designated by thenumeral 60. The power winch 27 maintains tension on cable 28 until allof the flanges 22 have been bolted and welded together.

The surface leg 20A, as illustrated in FIG. 5, contains an access tubeconnected into the upper section 1 1 to permit a welder access to thejoint connecting the upper and lower sections to weld flanges 22 ofthose sections together. The access tube 70 is also shown in FIG. 6. Acap 71 for access tube 70 may be provided to prevent water or othermatter from entering the legs through the access tube when no weldingoperations are being conducted. FIG. 5A shows a similar access tube 72connected into submerged leg 20B adjacent flange 22 of lower section 14.Either access tubes 70 or 72 may be connected into the legs of either ofthe sections 11 or 14.

Referring now to FIGS. 6, 7 and 8, it will be seen that the legs 20A and20B of each of the sections 11 and 14 are each provided with two sets ofdiaphragms 40 and 41 adjacent both ends thereof. Diaphragm 40 may beconstructed of plastic or other flexible material and is provided toafford buoyancy to the legs while diaphragm 41 may be constructed of anyof a number of common construction materials and acts as a safety backupfor diaphragm 40. Both diaphragms are flexible to some extent and arefrangible or rupturable for purposes described hereinafter. The sets ofdiaphragms form a watertight compartment 42 in each of the legs of eachof the sections. Connected to each end of the legs 20A and 20B andfluidly communicating with the chambers 42 are sea cocks 43 foradmitting sea water into the compartments when desired. The sea cocks 43are operated by motor means 44 which by fluid power lines 45 are eachconnected to a common junction box or manifold 46 which is attached tothe upper end of one of the legs 20A of the upper section 11 as shown inFIG. 8. The lines 45 of the upper section 11 and those of the lowersection are joined together by connector means 48, as, shown in FIG. 9,after the two sections have been unitized. The sea cock at one end ofcompartment 42 acts as a flooding valve and the one at the other end asan air escape means. The legs may be divided into several compartmentsif desired with each provided with two sea cocks such as 43'. The legs20A and 20B of each section are provided with spaced apart centralizersmeans such as pile guides 50. Each section may have a door or doors (notshown) in each leg adjacent the flanges 22 through which a welder mayenter to weld the flanges together from the interior of the legs 20A and208 as will be explained in more detail with respect to FIGS. l5. Thedoor may be previously formed or maybe cut into legs A and 20B and thenwhen welding is completed welded shut to close such entrances to legs20A and 208. Of course, water must be removed after the door is openedand the legs 20A and 20B kept free of water until deliberately flooded.

The power winch 27 is now removed from the structure and a power conduitline 45 as shown in FIG. 3 is connected between the power source meanson barge 23 and the junction box or manifold means 46 on the upper endof structure 60.

The crane lines 26 are then connected to the upper end of the structure60 and the assembly is now in position to begin flooding of the legs 20Aand 20B.

As the sea cocks are opened remotely from the barge 23 sea water entersthe compartment 42 of legs 20A and 20B the jacket 60 rotates to theposition shown in FIG. 3 with the upper end thereof controlled by thecrane 24 so that it sinks gently to the ocean floor with the upper endof the structure extending above water as shown in FIG. 4. The extensiondistance above the water surface may be anywhere from about 10 to 100feet as may be desired.

Piling 61 is then run in through each of the legs 20A and 20B of thestructure and by means not shown is driven into the ocean floor asubstantial depth to anchor the structure. As the piling is run throughthe legs, it ruptures and passes through the diaphragms and 41. Afterthe structure 60 has been anchored, a deck section 70 positioned by thecrane 24 is connected to the upper end of the structure.

Referring to FIGS. 10 to 15, the two sections, 11 and 14, are launchedand moved or pulled together as described with respect to FIGS. 1 and 2(please note that the upper and lower sections shown in FIGS. 10 and 11are reversed from the showings in FIGS. 1 and 2 and 5 to 9). Accesstubes 70', each provided with a cap 71, are connected to surface legs20A of lower section 14 and access tubes 72', each provided with asuitable cap 73, are connected into each of the submerged legs 20B ofupper section 11. These tubes are connected into legs 20A and 208 nearflanges 22 of those legs. Whether these tubes are located on the upperor lower sections is a matter of choice.

An alignment and latching, mating guide means generally designated 74are mounted on each of the legs to be connected together in making upthe sections. A guide member prong 75, shown connected by suitablesupport brackets 76 to surface leg 20A of lower section 14 is conicallyshaped and provided with latches 77. A

' connected to each submerged leg 20B of upper section 11 by brackets91. Guide prong and guide sleeve 80 are longer than guide prongs andguide sleeve 90. The differences in the sizes of the guide prongs on thesurface legs and guide prongs on the submerged legs are to ensure thatthe submerged legs are properly aligned before engagement of guideprongs 85 in guide sleeves 90. Once guide prongs 75 are engaged in guideI sleeves 80, the surface legs are properly aligned and the lowersubmerged legs are also generally aligned properly and final, precisealignment is achieved by the guide prongs 85 and guide sleeves 90.

FIG. 10 illustrates the upper and lower sections being brought together.FIG. 11 shows upper and lower sections engaged and fully made up. FIG.12 shows the guide prongs and guide sleeves in more detail. The flanges22 are the same as those previously described with respect to FIG. 5.

To facilitate connection of access tube 72' into legs 20B guides areconnected to cross struts 16 and to upper or surface legs 20A. Seatingtubes 96 shown more clearly in FIG. 13 make a sealing connection at 97with the lower end of access tubes 72' after they have been run inthrough guides 95. Seating tubes 96, as shown in FIGS. 14 and 15, arewelded to the sumberged legs 208. At the connection of tubes 96 andtubes 20B, manhole openings 98 are formed in tubes 208.

In operation, after sections 11 and 14 are connected together and boltedto each other and properly sealed as described herein, water is pumpedout of legs 208. Then a welder, as illustrated in FIG. 13, is loweredthrough access tube 72' into leg 20B adjacent flanges 22 which are shownhave been sealed and bolted together. The welder then welds the twosections of leg 20B together from the interior of the legs. All of thelegs 20B are welded in that manner. As illustrated in FIG. 15, after thewelding of the legs has been com pleted, the welder may then coveropening 98 with a plate 99 and weld the plate to sealingly closeopening- 88. If desired, access tube 72 may then be removed. Legs 20Aare welded together in a similar manner. The welder is lowered into aleg 20A through access tube 70 and welds the two sections of leg 20Atogehter from the interior of the legs. All of the legs 20B are weldedin that manner.-

Commercially available means other than bolts may be employed to securethe sections together in order to effect proper sealing of the sectionsprior to pumping out the water. Under some circumstances the guideprongs and guide sleeves alone, without bolts or other type connectingmeans, could achieve sufficient sealing of the sections to permitpumping out of water and welding.

Other changes and modifications may be made in the illustrativeembodiments of the invention shown and/or described herein withoutdeparting from the scope of the invention as defined in the appendedclaims.

It will be clear from the foregoing description taken with the drawingthat a new, useful, unobvious and therefore patentable result isobtained in unitizing and installing jackets to support offshorestructures in waters of great depths.

The nature and objects of the present invention having been fullydescribed and illustrated and the best mode and embodiment contemplatedset forth, what we wish to claim as new and useful and'secure by LettersPatent is:

1. A method of unitizing an offshore jacket for an offshore platform inwater comprising:

fabricating an offshore jacket having at least three legs and at leasttwo sections; launching said sections into said water such that each isseparately floating, each section having sufficient buoyancy to maintainat least one leg at the waters surface, the remaining leg or legs beingsubmerged;

aligning the companion legs of said sections and drawing said sectionstogether while floating said sections in said water;

, guiding said surface legs on said sections into alignment prior toguiding said submerged legs on said sections into alignment to ensureproper alignment of said submerged legs.

2. A method as recited in claim 1 in which the legs of said sections areconnected .together sealingly and welded together from the interior ofsaid legs;

3. A method as recited in claim 2 in which said sections are boltedtogether from the exterior of said legs prior to welding said legstogether.

4. A method as recited in claim 3 in which said welds made within theinterior of said legs are accomplished by a welder entering the legs ofsaid sections and moving to the habitat where the weld is to be made andmaking such weld.

5. A method of unitizing an offshore jacket in deep water and forlocating an offshore platform therein comprising:

fabricating an offshore jacket having at least three legs and at leasttwo sections, said jacket legs when connected together and located insaid water extending from water bottom to above water level;

launching said sections into said water such that each floatsseparately, each section having only sufficient buoyancy to maintain atleast two legs at the waters surface, the remaining legs beingsubmerged;

aligning the legs of said floating sections and drawing said floatingsections together,said surface legs on said sections being aligned priorto alignment of the submerged legs; securing said legs together; and

sinking said connected sections by decreasing the buoyancy of said legsuntil said jacket is in an upright position resting on water bottom andextending above water level.

6. A method as recited in claim 5 in which the legs of said sections areconnected together sealingly and welded together from the interior ofsaid legs.

7. A method as recited in claim 6 in which the legs of said sections arebolted together from the exterior of said sections.

8. A method as recited in claim 7 in which welders enter said legsadjacent the habitat of the connection of said legs to each other andthen weld said legs together.

9. A method as recited in claim 5 including driving piling through saidlegs to anchor said offshore jacket on water bottom.

10. A method of unitizing an offshore jacket in water which comprises:

fabricating an offshore jacket having at least three legs and at leasttwo sections;

launching said sections into the water such that each is separatelyfloating, each section having sufficient buoyancy to maintain at leastone leg at or above the waters surface, the remaining leg or legs beingsubmerged; aligning and drawing said floating sections together;sealingly connecting companion legs of said sections together from theexterior of said legs;

pumping water from said connected legs; and welding the legs of saidsections together from the interior of said legs including the submergedas well as the surface legs.

11. A method as recited in claim 10 in which a welder enters said legsto the habitat of the joint to be welded and welds said legs togetherfrom the interior thereof.

12. A method of unitizing an offshore jacket in deep water and forlocating an offshore platform which comprises: v

fabricating an offshore jacket having at least legs and at least twosections; floating each of said sections to a selected water location onat least one vessel;

launching said sections into the water such that each is separatelyfloating, each section having sufficient buoyancy to maintain at leastone leg at or above the waters surface, the remaining leg or legs beingsubmerged;

aligning said sections and drawing said sections to gether;

sealingly connecting companion legs of said sections together from theexterior of said legs;

pumping water from said connected legs;

welding the legs of said sections together from the interior of saidlegs including the sumberged as well as the surface legs; and

sinking said connected sections by decreasing the buoyancy of said legsuntil said jacket is in an upright position resting on water bottom andextending to above water level. f

13. A method as recited in claim 12 in which said legs are weldedtogether by a welder entering said legs and moving to the habitat wherethe legs are to be welded together and making such welds.

14. A method as recited in claim 12 including driving piling throughsaid legs to anchor said offshore jacket on water bottom.

three

1. A method of unitizing an offshore jacket for an offshore platform inwater comprising: fabricating an offshore jacket having at least threelegs and at least two sections; launching said sections into said watersuch that each is separately floating, each section having sufficientbuoyancy to maintain at least one leg at the water''s surface, theremaining leg or legs being submerged; aligning the companion legs ofsaid sections and drawing said sections together while floating saidsections in said water; guiding said surface legs on said sections intoalignment prior to guiding said submerged legs on said sections intoalignment to ensure proper alignment of said submerged legs.
 2. A methodas recited in claim 1 in which the legs of said sections are connectedtogether sealingly and welded together from the interior of said legs.3. A method as recited in claim 2 in which said sections are boltedtogether from the exterior of said legs prior to welding said legstogether.
 4. A method as recited in claim 3 in which said welds madewithin the interior of said legs are accomplished by a welder enteringthe legs of said sections and moving to the habitat where the weld is tobe made and making such weld.
 5. A method of unitizing an offshorejacket in deep water and for locating an offshore platform thereincomprising: fabricating an offshore jacket having at least three legsand at least two sections, said jacket legs when connected together andlocated in said water extending from water bottom to above water level;launching said sections into said water such that each floatsseparately, each section having only sufficient buoyancy to maintain atleast two legs at the water''s surface, the remaining legs beingsubmerged; aligning the legs of said floating sections and drawing saidfloating sections together, said surface legs on said sections beingaligned prior to alignment of the submerged legs; securing said legstogether; and sinking said connected sections by decreasing the buoyancyof said legs until said jacket is in an upright position resting onwater bottom and extending above water level.
 6. A method as recited inclaim 5 in which the legs of said sections are connected togethersealingly and welded together from the interior of said legs.
 7. Amethod as recited in claim 6 in which the legs of said sections arebolted together from the exterior of said sections.
 8. A method asrecited in claim 7 in which welders enter said legs adjacent the habitatof the connection of said legs to each other and then weld said legstogether.
 9. A method as recited in claim 5 including driving pilingthrough said legs to anchor said offshore jacket on water bottom.
 10. Amethod of unitizing an offshore jacket in water which comprises:fabricating an offshore jacket having at least three legs and at leasttwo sections; launching said sections into the water such that each isseparately floating, each section having sufficient buoyancy to maintainat least one leg at or above the water''s surface, the remaining leg orlegs being submerged; aligning and drawing said floating sectionstogether; sealingly connecting companion legs of said sections togetherfrom the exterior of said legs; pumping water from said connected legs;and welding the legs of said sections together from the interior of saidlegs including the submerged as well as the surface legs.
 11. A methodas recited in claim 10 in which a welder enters said legs to the habitatof the joint to be welded and welds said legs together from the interiorthereof.
 12. A method of unitizing an offshore jacket in deep water andfor locating an offshore platform which comprises: fabricating anoffshore jacket having at least three legs and at least two sections;floating each of said sections to a selected water location on at leastone vessel; launching said sections into the water such that each isseparately floating, each section having sufficient buoyancy to maintainat least one leg at or above the water''s surface, the remaining leg orlegs being submerged; aligning said sections and drawing said sectionstogether; sealingly connecting companion legs of said sections togetherfrom the exterior of said legs; pumping water from said connected legs;welding the legs of said sections together from the interior of saidlegs including the sumberged as well as the surface legs; and sinkingsaid connected sections by decreasing the buoyancy of said legs untilsaid jacket is in an upright position resting on water bottom andextending to above water level.
 13. A method as recited in claim 12 inwhich said legs are welded together by a welder entering said legs andmoving to the habitat where the legs are to be welded together andmaking such welds.
 14. A method as recited in claim 12 including drivingpiling through said legs to anchor said offshore jacket on water bottom.